Posts Tagged ‘Boogie’

I don’t have time to type right now, but here are the images from the analysis for a 2 Channel Orange, 3 Channel Vintage on ch 2, and 3 Channel Vintage on ch 3. The responses of the 2 Channel Orange and 3 Channel Vintage on ch 2 are very close. Other factors could influence the differences between them.

I very quickly drew the negative feedback filter controlled by the presence control when using Vintage mode on a 2001 3 Channel Dual Rectifier. The red line represents the -3 dB half boost mark from the point of the most filtering. I tried drawing the entire phase inverter, but it didn’t make a difference on the plots, so I removed it and kept it simple.

R2 is being instructed to act as a variable resistor with 11 points to represent each 30 degrees of travel from 0 -10 on the control. Anytime a part of the plot goes below the red line, the feedback is lessened by quite a bit and those frequencies pass the phase inverter more easily. The maroon line on each picture is representing the control being at maximum and a massive amount of the frequency band is passing easily. (more…)

Like this:

In some of the articles, I made statements regarding a possibility of mild power amp drive, because I had not had time to really dig into the power amp to confirm or deny it, and due to the sound of Modern mode. The power amp does not overdrive. If you come across anything relating to this, any descriptions should be discarded if they contradict the following paragraphs.

Modern has some distortion present, but it isn’t clipping distortion; It’s regular ol’ harmonic distortion, which is otherwise known as “the tube sound”. I don’t have time or energy to get into it, but the power amp is designed to stay as clean as possible, but tubes do not always amplify in a “linear” way. This adds curvature to the sound waves, distorting them by bending (coloring the sound). (more…)

I had just a few thoughts come to mind regarding modifying amps, modifying EQ, or creating your own.

It’s a fact that Mesa Engineering uses two modified forms of the Marshall tone stack for their Dual Rectifier series. Compared to a classic Marshall tone stack, the Vintage/Raw tone stack moves the center of the “Mid” control down in frequency and has more attenuation. This carves out some of the meatier part of the guitar frequency to make room for the massive lows and a high-mid emphasis. The tone stack enabled for Channel 3 Modern has boosted upper-mids, but has a very similar, low-to-low-mid frequency response. (more…)

On the back of every Mesa Engineering Dual Rectifier, there are 2 switches to select options for the power supply. One of these is to select Bold and Spongy and affect overall voltage to the amplifier, with Bold being full power and Spongy reducing power by about 20%. The other switch is used to select the rectification: Silicon or Tube. Selecting Tube reduces power by nearly 10%, since the tube has losses when it conducts. There are 4 options for running the power supply:

Bold and Silicon

Bold and Tube

Spongy and Silicon

Spongy and Tube

Before I get to decisions for selecting power supply options, we should cover some facts and history. Along the way, we’ll learn basic information about the differences between these options. (more…)

(Note: During the initial 5 year period of warranty, using tubes other than those branded by Mesa will void the warranty of your amp. This article is meant for people who have amps which are not under warranty.)

Mesa’s 6L6GC STR tubes are manufactured in China for Ruby Tubes. It is a reproduction of the classic Sylvania 6L6GC STR. Mesa buys a big batch from Ruby, tests them, keeps the tubes that meet their requirements, and sends back the tubes which fall out of range. Ruby’s matched version of this same tube is the 6L6GCMSTR. It costs considerably less than Mesa’s tubes. (more…)

I’ve been experimenting with making Channel 3 a fuzz tone for a long time, but recently got just the setting I wanted. This kind of setting gets close to “Dazed And Confused” and sounds good with “Purple Haze”. Being tube, instead of transistor, it’s a little softer, but the Presence can dial in the edge a person needs for fuzz bliss.

Yellow is the Modern setting as described above with no treble and full mids. Green reduces Bass to 11:00.

The way that old, germanium transistor fuzzes would clip is awfully close to the way the cold clipping circuit works in these Marshall/Soldano types of circuits and the Recto has the bottom end to really sound huge.

I found this Channel 2 Raw setting to be a match for the fuzz tone. It’s bright, with plenty of bottom, and crunches up quite nicely. Both dirty channels get cleaner as guitar volume is rolled back, but, like a Tonebender, Channel 3 never gets “squeaky clean”, but it does make a nice half-clean sound, since the treble is flattened.

I was spying a schematic for a Mesa Engineering Stiletto and noticed some very interesting details regarding the signal path. When the Crunch mode is selected for either channel, the relays pull the cold clipping stage out of the circuit. This creates a modified copy of a Model 1959 JCM 800. (more…)

I know I previously stated I would discontinue writing about mods, but this one has been in the back of my head for a long time. A lot of the grind produced by the cold clipping stage is due to the presence of third harmonics (H3). By forcing the idle point to be so close to grid current limiting, the amount of information loss from the distortion is going to produce it.

Yesterday, I was playing around with the Trioda load line program and found an interesting effect. With the parameters set about where the resistances would be for V2b, the cold clipping stage, I was adjusting the cathode value. As the cathode resistance moves from 39k to 10k, the amount of H3 falls to an amount which would become inaudible. (more…)

We’ve looked at the input and Clean, the voicing and Gain control, and V2. Now, it is time to examine V3, the coupled cathode follower. I urge you to read about cathode followers if you do not understand how they work and wish to learn more.

The biggest things for a novice to know are:

A cathode follower is usually used to lower impedance to drive a tone stack or an effects loop.

The cathode of the second tube follows the voltage on its grid closely (hence “cathode follower”).

The first tube provides amplification of the signal and stability to the cathode follower.

When coupled (wired together), the two tubes act like one (mostly). (more…)